In order to reduce costs in connection with ship transports it is of the greatest importance to reduce the periods of the boats lying still in port. Harbour dues and charges of utilized harbour equipment are very high. Thus, the cranes of the ships have tended to become ever bigger and more efficient. Nowadays they must be able to handle big standard cargoes intended to be loaded and transported on special ships with maximum stowing capacity. In this connection it may be worth mentioning that the ships are sometimes so dimensioned that they can pass the locks in certain canals only by a margin of a few centimeters along the sides and in stem and stern.